1. Field of the Invention
This invention relates to a method and apparatus for decreasing undesirable emissions in the exhaust of a compression ignition (diesel) engine, and more particularly, to a new and improved method and apparatus for decreasing total particulates and oxides of nitrogen (NO.sub.X) from the exhaust of the diesel engine by introducing oxygen enriched air and an increased quantity of fuel and by retarding the injection timing of the diesel engine.
2. Background of the Invention
Compression ignition (diesel) engines typically have high exhaust emissions, such as particulates (for example, carbon soot and volatile organic compounds), visible smoke, and oxides of nitrogen (NO.sub.X). Environmental Protection Agency (EPA) emissions standards for future automobiles, trucks and locomotive diesel engines require simultaneous reduction of NO.sub.X and total particulate emissions to very low levels. This tends to be difficult to achieve because of the inherent tradeoffs between lowering both total particulates and NO.sub.X emissions from a diesel engine. While it is possible in a diesel engine to reduce total particulate emissions and to improve power density performance by using oxygen enriched intake air, such oxygen enriched intake air tends to also increase the amount of NO.sub.X in the exhaust being emitted from the diesel engine.
In the case of both diesel and spark ignition engines, exhaust gas recirculation (EGR) systems have been used as one method of decreasing NO.sub.X emissions. When the gases from the EGR system are about 50% of the intake air, oxygen concentration is decreased from about 21% to about 14%. The decrease of NO.sub.X by the use of EGR systems tends to vary depending on the rate, temperature and water content of the EGR gases, injection timing, and air-fuel ratio of the intake to the engine. However, there are limits as to the amount of exhaust gases that can be reintroduced into the engine before power output and fuel economy are adversely affected. Such reintroduction of exhaust gases can also cause wear problems and oil contamination, particularly in the case of diesel engines where the recirculated gases include soot particles.
Other attempts have been made to control the amount of NO.sub.X being emitted from the exhaust of an engine. In order to control the amount of NO.sub.X actually generated by the engine, the amount of oxygen and nitrogen included in the intake of air of the engine has been controlled (see, for example, U.S. Pat. No. 5,649,517 that is assigned to the same assignee of record as the present application). On the other hand, attempts have been made to lower the level of NO.sub.X in such exhaust gases or emissions of an engine by injecting into the exhaust gases of the engine monatomic-nitrogen induced by a pulse arc (see, for example, U.S. Pat. Nos. 5,526,641 and 5,640,845 that are assigned to the same assignee of record as the present application). While these systems tend to decrease the level of NO.sub.X in engine exhaust gases, they do not tend to decrease the total particulates that are present in those exhaust gases.
Accordingly, it is an object of the present invention to provide a new and improved method and apparatus for decreasing both total particulates and NO.sub.X emissions in the exhaust of a diesel engine.
It is another object of the present invention to provide a new and improved method and apparatus for decreasing both total particulates and NO.sub.X emissions in the exhaust of a diesel engine while enhancing the power generated by the engine by introducing oxygen enriched air into the air intake of the engine and by increasing the quantity of fuel injected into the engine while simultaneously controlling (retarding) the engine injection timing.
It is yet another object of the present invention to provide a new and improved method and apparatus for reducing the amount of total particulates and NO.sub.X in the exhaust of a diesel engine while enhancing the power generated by the engine by introducing oxygen enriched air into the air intake of the diesel engine by diverting at least a portion of the intake air through a selectively permeable membrane so that ambient air and oxygen enriched air can be selectively supplied to the engine intake manifold, by increasing the amount of fuel introduced into the engine and by retarding the engine injection timing.